By the end of 2015 Russia's Northern Fleet is to deploy a novel acoustic detection system, which would verify that its newest stealth subs are as quiet as they should be to avoid being spotted during combat missions.

The system, called
Batareya (battery), is currently in its final stages of
development, senior researcher at the VNIIFTRI - an institute
that develops various instruments for the Russian military -
Sergey Tsigankov told TASS.

“It will detect acoustic signatures of nuclear submarines,
first of all those of the fourth generation,” he said.
“We are completing a prototype now and plan to deliver it to
the Northern Fleet in the White Sea this year.”

Detecting the signature of a modern stealth submarine that was
built to be as quiet as possible is a difficult task. In fact
their noise levels are usually lower than the ambiance of the sea
itself. This may be good when a sub is on a combat mission trying
to avoid detection, but gives a headache to its engineers trying
to determine which equipment is the noisiest and should be
muffled further.

The brute force approach to the problem is to have a testing
range with as few ambient sounds as possible. Norway's Heggernes
facility is used to check acoustic signatures of the submarines
of European NATO members. The US Navy finished a new facility in
Ketchikan, Alaska, several years ago.

The new Russian system can serve the same purpose without costly
infrastructure investment, the producer said. It can pick sound
signatures about two times less noisy than the ambient sounds.

The Northern fleet is to deploy Batareya hydrophones some 30 km
off coast its submarine base, Tsigankov said. The data would be
transmitted via a fiber optic cable.

“We chose this way for transmission because no western nation
currently has a technology to intercept data from a fiber optic
cable underwater. This channel is well-protected from
surveillance,” he explained.